Hydrogen Energy: An Energy Carrier, Not an Energy Source
Almost every disagreement about hydrogen dissolves once one distinction is made: hydrogen is not a source of energy, it is a way of carrying it. Nobody mines hydrogen. The energy in a kilogram of hydrogen was put there by something else - a gas reformer or an electrolyser - and some of it was lost on the way in.
Where Hydrogen Comes From
Hydrogen is the most abundant element in the universe and almost absent as a free gas on Earth, because it is light enough to escape the atmosphere and reactive enough to end up bound in water and hydrocarbons. Every kilogram used industrially has been prised out of one of those compounds.
Steam methane reforming does it with natural gas and steam at around 800 degrees, producing hydrogen and carbon dioxide. It is mature, cheap and responsible for the majority of world production - and it emits roughly nine to twelve tonnes of carbon dioxide per tonne of hydrogen. Adding carbon capture to that process is what the term blue hydrogen describes; how much is actually captured varies by plant and is the substance of most arguments about the colour.
Electrolysis splits water with electricity instead. It has been understood since the early nineteenth century and is a mature technology, but it is more expensive than reforming wherever gas is cheap. When the electricity comes from renewables the product is called green hydrogen, and the carbon intensity of the electricity is what the label really tracks - electrolysis powered by a coal grid produces hydrogen dirtier than reforming.
A smaller category, white or natural hydrogen, refers to geological accumulations produced by water reacting with iron-rich rock. Exploration has intensified since 2023. Whether it exists in commercially recoverable quantities is an open question rather than an established resource.
The Efficiency Chain
Every step in a hydrogen pathway takes a cut, and the cuts multiply. Start with 100 units of electricity. A modern electrolyser converts perhaps 70 of those into hydrogen. Compressing it to 700 bar for transport or storage costs roughly another 10 percent of the energy content. Converting it back to electricity in a fuel cell at 50 to 60 percent efficiency leaves somewhere between 30 and 40 units of the original 100.
The comparison that matters is the alternative. A lithium-ion battery returns about 90 units of the same 100, and a direct wire returns about 95. This is why hydrogen loses badly for passenger cars and home heating, where a battery or a heat pump does the same job at two to three times the efficiency.
But efficiency is not the only currency. Hydrogen stores chemically, so it can sit for months without self-discharge, and it can be moved in quantities and over distances that batteries cannot approach. For seasonal energy storage, and for uses where the hydrogen atom itself is needed rather than the energy, the round-trip loss is beside the point.
What Hydrogen Is Actually For
The largest existing use is ammonia for fertiliser, which consumes roughly half of world production. There is no way to make ammonia without hydrogen; the Haber-Bosch process requires the atom itself. Decarbonising fertiliser therefore means decarbonising hydrogen, with no electrification alternative available.
Steel is the case most often cited and the most consequential. Conventional steelmaking uses coke to strip oxygen from iron ore, releasing carbon dioxide as an unavoidable product of the chemistry. Hydrogen can perform the same reduction and produce water instead. Direct reduction plants running on hydrogen are operating at demonstration scale in Sweden and under construction in Germany. Steel accounts for roughly seven percent of global carbon dioxide emissions, so the stakes are large.
Shipping and aviation are the transport cases where batteries struggle with energy density over long distances, and ammonia or hydrogen-derived fuels are among the few candidates. Refining, which already consumes large volumes of hydrogen to remove sulphur, is a existing market rather than a new one.
What these have in common is that no wire reaches them and no battery is dense enough. That is the honest test for any proposed hydrogen application, and a good deal of the enthusiasm of the early 2020s failed it.
Moving and Storing It
Hydrogen carries about three times the energy per kilogram of petrol and about a quarter of the energy per litre when compressed to 700 bar. That combination - superb by mass, poor by volume - dictates everything about handling it.
Compression to 350 or 700 bar is the usual road transport solution. Liquefaction at minus 253 degrees achieves higher density but consumes 30 percent or more of the energy content, which is why it is reserved for cases like rocketry. Converting hydrogen to ammonia for shipping and cracking it back at the destination is under active development for intercontinental trade.
Pipelines can carry hydrogen, and some existing natural gas networks can be converted, though hydrogen embrittles certain steels and leaks through seals that hold methane. Blending small percentages into existing gas grids is being trialled in several countries; it reduces emissions proportionally less than the blend fraction suggests, because hydrogen carries less energy per unit volume.
Underground salt caverns are the established large-scale storage option and have held hydrogen commercially for decades in Texas and the United Kingdom. They are the reason seasonal storage is discussed seriously at all: a cavern can hold energy at a scale and cost per kilowatt-hour no battery approaches.
Frequently asked questions
Is hydrogen a source of energy?
No. It is a carrier. There are no hydrogen deposits to extract in useful quantity, so every kilogram is manufactured from methane or water using energy from somewhere else, and some of that energy is lost in the making. Its value lies in storing and moving energy, not in providing it.
What do the colours mean?
They describe how the hydrogen was made. Grey comes from methane with the carbon dioxide vented, blue from methane with carbon capture, green from electrolysis using renewable electricity. Pink refers to electrolysis powered by nuclear. The molecule is identical in every case; the label describes its history.
Why not use hydrogen for cars?
The efficiency chain. Electricity to hydrogen to motion returns roughly a quarter to a third of the input energy; a battery electric vehicle returns around three quarters. Where a battery is dense enough for the job, it wins on physics before any question of infrastructure arises.
How much hydrogen does the world use today?
Around 95 million tonnes a year, almost entirely as an industrial feedstock - ammonia for fertiliser, refining and methanol. Energy uses are a small fraction of that, which means the first task of decarbonising hydrogen is cleaning up production that already exists.
Is hydrogen dangerous?
It is flammable over a wide range of concentrations and burns with a nearly invisible flame, so it requires different handling from conventional fuels. It is also extremely light and disperses upward rapidly, which reduces pooling risk. Industry has handled it at scale for a century; the safety questions are about new consumer-facing uses rather than the substance itself.
